Taking ibuprofen and acetaminophen on daily basis while weight lifting may increase muscle mass and strength, says new research by Ball State University.

A study of male and female participants found that taking regular daily doses of one of the two pain relievers may substantially increase the amount of quadriceps muscle mass and strength during three months of intense weight lifting.

Physiologists Todd Trappe and Chad Carroll from Ball State's Human Performance Laboratory (HPL) presented their findings April 6 at the Experimental Biology 2008 conference in San Diego. The presentation was part of the scientific program of the American Physiological Society (APS).

Thirty-six men and women, between age 60 and 78 years, were randomly assigned to daily dosages of either brand versions of ibuprofen, acetaminophen or a placebo. The dosages were identical to those recommended by the manufacturers and were selected to most closely mimic what chronic users of these medicines were likely to be taking.

Subjects participated in three months of weight training that included 15- to 20-minute sessions three times a week in the Human Performance Laboratory.

"Over three months, the chronic consumption of ibuprofen or acetaminophen during resistance training appears to have induced intramuscular changes that enhance the metabolic response to resistance exercise," Trappe said. "This allows the body to add substantially more new protein to muscle."

The researchers now are analyzing muscle biopsies taken before and after the three-month period of resistance training.

Going into the research project, Trappe and Carroll, an HPL post-doctorate fellow, knew various studies that training at this intensity and for this time period would significantly increase muscle mass and strength.

As they expected, the placebo group showed such increases, but researchers were surprised to find that the groups using either ibuprofen or acetaminophen did even better. The most recent study appears to contradict previous findings.

An earlier research project from the laboratory, measuring muscle metabolism — or more precisely, muscle protein synthesis, the mechanism through which new protein is added to muscle — had looked at changes over a 24-hour period. This acute study found that both ibuprofen and acetaminophen had a negative impact, by blocking a specific enzyme cyclooxygenase, commonly known as COX.

Trappe said the study has implications for the elderly, who suffer from muscle loss as they age, and astronauts, who lose muscle mass and strength during long durations in space. HPL currently has research projects focusing on the adaptation to exercise in both groups.

Funding for the research came from the National Institutes of Health and a postdoctoral initiative award from APS.